Radiation therapy of a tumor is currently limited by the inability to follow the motion of the tumor during treatment. Magnetic resonance imaging (MRI) technique has the potential to provide good images of the tumor, fast enough to allow imaging during treatment. This would allow accurate dose deposition in the tumor and spare the surrounding tissue. Integration of MRI and Linear Accelerators (LINAC) opens new horizons in radiotherapy by improved lesion targeting, especially for moving organs. It may be desirable to provide systems for enhancing therapeutic efficiency with MRI technique.